American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index was unchanged in September, following a gain of 1.6% the previous month. In September the index equaled 132.6 (2000=100), the same as in August and a record high.  Compared with September 2013, the SA index increased 3.7%, down from August's 4.5% year-over-year gain. Year-to-date, compared with the same period last year, tonnage is up 3.2%. The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 135.8 in September which was 1.7% above the previous month (133.5).  "September data was a mixed bag, with retail sales falling while factory output increased nicely," said ATA Chief Economist Bob Costello. "As a result, I'm not too surprised that truck tonnage split both of those readings and remained unchanged." "During the third quarter, truck tonnage jumped 2.4% from the second quarter and surged 4% from the same period last year," Costello said.  He also noted that the third quarter average was the highest on record. Trucking serves as a barometer of the U.S. economy, representing 69.1% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 9.7 billion tons of freight in 2013. Motor carriers collected $681.7 billion, or 81.2% of total revenue earned by all transport modes. ATA calculates the tonnage index based on surveys from its membership and has been doing so since the 1970s. This is a preliminary figure and subject to change in the final report issued around the 10th day of the month. The report includes month-to-month and year-over-year results, relevant economic comparisons, and key financial indicators.